z
Abbreviation with 5 meanings
| Stands for | z-score |
|---|---|
| Meanings | 5 |
| Categories | Units & Measurements |
| Also written | Z |
z has five meanings. The most common are z-score (statistics) and Zulu time (UTC) (time zone); it can also stand for Integers, Zetta- (sextillion) and Zepto- (sextillionth).
Meanings of z at a glance
| # | z stands for | Context |
|---|---|---|
| 1 | z-score | Units & Measurements › Statistics |
| 2 | Zulu time (UTC) | Units & Measurements › Time Zone |
| 3 | Integers | Units & Measurements › Math |
| 4 | Zetta- (sextillion) | Units & Measurements › Metric and SI Unit |
| 5 | Zepto- (sextillionth) | Units & Measurements › Metric and SI Unit |
1. z-score
Units & Measurements · Statistics Abbreviations
The number of standard deviations a value lies above or below the mean: z = (x − mean) / SD. A z-score of 2 means a value two standard deviations above average, higher than about 97.7 percent of a normal distribution.
Example: Her score of 130 corresponds to z = 2.0 on a test with mean 100 and SD 15.
Standardizing to z-scores lets different scales be compared, such as height and weight percentiles. Z-tests use the standard normal distribution when the population SD is known or samples are large. Bone-density scans report standardized T-scores and Z-scores, and Excel's STANDARDIZE function computes z directly.
2. Zulu time (UTC) (Z)
Units & Measurements · Time Zone Abbreviations
Military and aviation designation for UTC, written as a Z after a time, as in 1430Z. Weather reports, flight plans and NOTAMs worldwide are timed in Zulu so that pilots crossing many zones share one clock.
Example: METAR KJFK 041451Z 27012KT 10SM FEW050 12/M03 A3012
In the military system, each time zone has a letter from A to Z, and the zero-offset zone is Z, spoken "Zulu" in the NATO phonetic alphabet; local time is designated J, "Juliet". The trailing Z in ISO 8601 timestamps such as 2026-11-04T09:00:00Z means the same thing. Pilots say "fourteen thirty Zulu".
3. Integers (Z)
Units & Measurements · Math Abbreviations
Blackboard-bold ℤ names the set of integers, ..., −2, −1, 0, 1, 2, .... The letter comes from German Zahlen, "numbers".
Example: The equation 2x = 7 has no solution in Z, but it does in Q.
Variants include Z+ for the positive integers and Z/nZ for the integers modulo n, the setting of modular arithmetic. In abstract algebra the integers are the standard first example of a ring. Unlike the natural numbers, Z is closed under subtraction.
4. Zetta- (sextillion) (Z)
Units & Measurements · Metric and SI Unit Abbreviations
Zetta- denotes 10^21 and is used for zettabytes of data created worldwide and for zettajoules of heat absorbed by the oceans in climate research. Annual global data creation is now estimated in the low hundreds of zettabytes.
Example: Analysts estimate the world now generates well over 100 ZB of data each year.
Adopted in 1991 at the 19th General Conference on Weights and Measures, together with yotta-, zepto- and yocto-. The name is based on Latin septem, seven (1000^7), with the s changed to z so that the symbol would not clash with s for second. Capital Z and lowercase z (zepto-) are 42 orders of magnitude apart.
5. Zepto- (sextillionth)
Units & Measurements · Metric and SI Unit Abbreviations
Zepto- (10^-21) was adopted in 1991. It turns up in single-molecule research and analytical chemistry, where a zeptomole is only about 600 molecules.
Example: The sensor detected the analyte down to about 1 zmol, a few hundred molecules.
Like zetta-, its name is based on Latin septem, seven (1000^-7), with s changed to z to avoid a clash with the symbol for second. Lowercase z is this prefix, and capital Z is zetta-, 10^21. Both were added at the same 1991 conference as yocto- and yotta-.
Related abbreviations
More statistics abbreviations
- a.s. – Almost surely
- ACF – Autocorrelation function
- AIC – Akaike information criterion
- ANCOVA – Analysis of covariance
- ANOVA – Analysis of variance
- ARIMA – Autoregressive integrated moving average
- ATE – Average treatment effect
- avg – Average
See all 88 statistics abbreviations →